The "th" Reveral Effect

I mentioned in a post awhile back that I was working with Isaiah on his "th" sound. He had previously used the "d" sound in place of "th", but I think that we have progressed far enough that he is using the "th" sound regularly without me having to remind him.

The problem is that...now he is starting to use the "th" sound in place of every "d" sound, even for words that start with "d"! I never would have expected this to happen, but maybe it's a sign of independence or self-motivation, just taking it to the next level. I notice it especially when he's using the words "do" or "does" sometimes he will say "thoo" or "thoes". Then I have to stop and correct him back to the "d" sound.

This is one of those things that is hopefully unique to Isaiah.